Numerous apparatus have previously been developed for the transdermal delivery of drugs and other medicinal compounds utilizing microneedle arrays. Microneedles have the advantage of causing less pain to the patient as compared to larger conventional needles. In addition, conventional subcutaneous (often intra-muscular) delivery of drugs via a needle acts to deliver large amounts of a drug at one time, thereby often creating a spike in the bioavailability of the drug. For drugs with certain metabolic profiles this is not a significant problem. However, many drugs benefit from having a steady state concentration in the patient's blood stream; a well-known example of such a drug is insulin. Transdermal drug delivery apparatus including microneedle arrays are technically capable of slowly administering drugs at a constant rate over an extended period of time. Alternatively, transdermal drug delivery apparatus including microneedle arrays may administer drugs at variable rates. Thus, transdermal drug delivery apparatus including microneedle arrays offer several advantages relative to conventional subcutaneous drug delivery methods.
There is a desire for microneedle arrays or assemblies that provide a new balance of properties.